Cathode-ray tube circuits



Patented Dec. 27, 1949 CATHODE -RAY TUBE CIRCUITS Arthur Henry Ashford Wynn, London, England, assignor, by mesne assignments, to Sylvania Electric Products Incorporated, Flushing, N. Y., a company of Massachusetts Application December 14, 1946, Serial No. 716,200 In Great Britain December 20, 1945 4 Claims.

This invention relates to circuits for cathode ray tubes.

In the operation of a cathode ray tube it is necessary to have a very high voltage supply, frequently of some 10,000 volts, this being used for the purpose of accelerating and focussing the electron beam which is directed towards the fluorescent screen. If a high velocity electron beam is allowed to impinge concentratedly upon a certain spot on the screen continuously for any considerable length of time it is found that the screen is damaged at that spot: it is therefore desirable, either that the beam should be kept in continuous movement, or that when the beam becomes stationary the accelerating or focussing voltages are reduced. In the case of a television receiver the deflection of the spot is eifected by the frame time-base and the line time-base.

It is an object of the present invention to provide interlocking between the high voltage supply and the deflecting means so that damage of the screen is avoided.

The following description relates to the accompanying drawing which shows the circuit of a high voltage supply generator for a television receiver, of which only the picture tube CRT, the line deflecting circuit L and the line deflecting coils LD are shown.

The circuit is that of a R. F. oscillator working at about 260 kc./s. and generating some 8 kv. The beam tetrode BT has a tuned anode circuit Ll, Cl, with the coil Ll inductively coupled to an output coil L2 and a tickler coil L3 in the grid circuit. The output coil L2 is in series with a rectifier RCI which is indirectly heated from a fourth coil L4. Normal anode potential to tube ET is supplied over the lead labeled to 13+, being of the order of 400 volts positive; while the high voltage output is available on lead labeled after having been smoothed by the smoothing network SMN. The circuit as so far described is in itself already known.

In accordance with the present invention the voltage to the screen grid of ET is derived from the line deflection wave generator L, coming from the line deflecting coils LD over lead LC to rectifier RC2. The voltage on the screen grid of BT may also be used to control the focussing of the cathode ray tube. As the screen of the oscillator valve is supplied by rectification of the voltage pulses across the line deflector coils, any failure of the line deflection wave generator will switch off the anode potential supply, and the anode potential supply oscillator can start to oscillate only after the line deflection wave generator has started to swing the electron beam.

The resistor SR. between the screen and cathode of the oscillator valve BT may be made variable and will then provide a control of the anode supply voltage. This control can then be used to give a fine manual adjustment of focus.

I claim: i.

1. In a cathode ray tube system having a source of wave energy for causing a cathode ray to be swept in one direction and a radio frequency oscillator for generating a high voltage supply for said cathode ray tube, means for deriving a control voltage for said oscillator from said source of wave energy and means for so applying said control voltage to said oscillator as to render said oscillator operative only when said source is operative.

2. In a cathode ray tube system having a source of wave energy for causing a cathode ray to be swept in one direction and a radio frequency oscillator including a tube having a control electrode, means for rectifying the oscillations generated by said oscillator to provide a direct potential for application to said cathode ray tube, and a rectifier coupled to said source of wave energy for deriving a control potential, said control potential being applied to said control electrode to render said oscillator operative only when said source is operative.

3. In a cathode ray tube system having a source of wave energy for causing a cathode ray to be swept in one direction and a radio frequency oscillator including a tube having a control electrode, a rectifier coupled to said oscillator to provide a direct potential for application to said cathode ray tube, a second rectifier coupled to said source of wave energy for deriving a control potential, and means for applying said control potential to said control electrode in such sense as to render said oscillator operative only when said source is operative.

4. In a cathode ray tube system having a source of wave energy for causing a cathode ray to be swept in one direction and a radio frequency oscillator including a tube having a control electrode and a screen electrode, a rectifier coupled to said oscillator to provide a direct potential for application to said cathode ray tube, and means coupled to said source of wave energy for deriving a control potential, and means for applying said control potential to the screen electrode of said oscillator tube to render said oscillator operative only when said source is operative.

ARTHUR HENRY ASHFORD WYNN.

(References on following page) REFERENCES CITED Number UNITED STATES PATENTS Name Date Vance Mar. 23, 1937 Goodrich Nov. 9, 1937' Number 4 Name Date Von Ardenne Sept. 2'7, 1938 Stocker May 28, 1940 Bowman-Manifold Aug. 6, 1940 White et a1; Nov.'19, 1940 Lyman Mar. 26, 1946 

